We will examine biochemical processes related to transmitter metabolism in identified Aplysia neurons and their dependence on neuronal function. In addition to specific biosynthetic enzymes, these processes largely involve membrane systems of the cell: storage occurs in granules or vesicles; turnover of transmitter substances depends critically on their subcellular localization; transport of transmitter apparently occurs in the axons only if it is packaged in vesicular form; release is thought to involve synaptic vesicles. Each of these processes presumably consists of a series of steps which we now hope to be able to analyze. In order to examine the mechanism of these individual processes and their possible functional modulation by neuronal activity, we plan specifically: 1) to study identified cholinergic and serotonergic neurons to trace the assembly, exit and axon transport of 3H-glycoproteins synthesized in the cell body after intrasomatic injection of 3H-fucose, and to relate specific 3H-glycoprotein components to the cholinergic and serotonergic vesicle and other membranous organelles using biochemical and radioautographic techniques; 2) to focus on the biochemistry of the storage granule, particularly in serotonergic cells, to obtain a detailed understanding of the involvement of membranous structures in storage, transport and release of transmitter; and 3) to develop a new assay for heterologous membrane functions in living Aplysia neurons.